Dissertations / Theses: 'Sedimentation modes'

1

Kurt, Nilufer, and nilf_k@yahoo com au. "A Study of Channelling Behaviour in Batch Sedimentation." RMIT University. School of Civil and Chemical Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061220.120258.

Full text

Abstract:

Batch sedimentation is a method that enables us to understand the mechanism of compaction and compression of sedimenting slurry. However, batch settling behaviour is a very complex phenomenon that is not easily described fully by a mathematical model. This causes unrealistically large empirical calculations when the thickener size estimations are required. Channelling, reverse concentration gradients and the initial concentration of the slurry have large effects on batch settling. Existing procedures do not provide clear relationships involving these three significant variables. In this study, batch sedimentation phenomena are examined in detail and possible explanations are given to clarify the complex behaviour using recent theories. Modern research has shown that channelling is an unwanted formation because channels can change the concentration at the bottom and top of the bed by carrying a great amount of flocs upwards. Batch sedimentation tests were performed using flocculated slurry of Calcium Carbonate at various initial concentrations such as 250 g/l, 500 g/l, 750 g/l and 1000 g/l to observe channelling and reverse concentration gradients. Flux plots for the batch system reveal behaviour which can be attributed to the upward flow of solids. In addition, photographic methods were used to observe settling processes, channelling mechanisms and flocs in the channels. One of the purposes of this work was to examine the phenomenological solid-liquid separation theory of Buscall and White (1987), which employs the material properties of the local volume fraction, compressive yield stress Py ()ö and hindered settling function R()ö to identify the material behaviour in batch sedimentation. Stepped-pressure filtration and batch settling tests were used to measure the material characteristics for the flocculated CaCO3 suspension. Experimental data were demonstrated using Height versus Time and Height versus Concentration graphs and displayed the possible region of reverse concentration gradients and channelling in the settling bed. Mathematical predictions adopted from Usher (2002) were performed employing material characteristics of the material and graphical documentations were presented. The results of mathematical predictions were compared to the experimental results and the modes of sedimentation explained by Lester et al. (2005). Fundamental theoretical models and experimental observations highlight that the main driving force for channelling is the high-pressure gradient at the bottom of the bed and the most important factors that cause channelling are high initial concentration of slurry and settling time. The predictions also show that the material and flocculant used for the batch settling tests demonstrate important effect on the settling process. The knowledge and information gained from this study is valuable to maximize the thickening process.

APA, Harvard, Vancouver, ISO, and other styles

2

Hernando, Louis. "Sédimentation de suspensions non-colloïdales poly-dispersés et concentrées." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14490/document.

Full text

Abstract:

De la pâte à dentifrice au moût de fermentation en passant par la peinture, le lit d’une rivière, le propergol d’un réacteur de fusée et le sang, les suspensions sont présentes dans de nombreux usages de notre vie courante. La maîtrise de leur mise en œuvre notamment nécessite la compréhension de leur comportement et constitue un des challenges de la recherche. Dans le présent travail de thèse, nous nous sommes intéressés au processus de sédimentation de suspensions concentrées de particules non-colloïdales et inertes dont la distribution de taille est mono, bi ou tri-disperse. Deux types de sédimentation ont été étudiés : la décantation et l’alimentation continue. L’objectif est de mener une étude expérimentale et dans une moindre mesure numérique pour caractériser de la façon la plus complète possible la sédimentation avec une attention particulière à la structure de l’écoulement et du dépôt, aux profils de concentration et à la détermination des modes de sédimentation. Les moyens expérimentaux utilisés sont les techniques usuelles de mesure bidimensionnelle (vélocimétrie laser et visualisation directe) qui autorisent l’acquisition de données d’intérêt pour des configurations où les particules évoluent dans le plan. Ces techniques laser ont été améliorées pour permettre le suivi simultané de populations de différentes particules et l’accès à des grandeurs diverses telles que le champ de vitesse de l’écoulement, la fraction volumique locale, et les vitesses des divers fronts de sédimentation. En parallèle, un outil numérique simple a été construit, utilisant la Dynamique Stokesienne et saisissant l’essentiel des phénomènes physiques mis en jeu menant à la modélisation des interactions hydrodynamiques From toothpaste to must of fermentation passing by painting, bed of a river, propellant of an rocket engine and blood, suspensions are present in many uses of our everyday life. The control of their implementation requires comprehension of their behavior and constitutes one of the challenges of nowadays research. In this work of thesis, we were interested in the sedimentation process of concentrated suspensions of non-colloidal and inert particles whose size distribution is mono, bi or tri-disperse. Two types of sedimentation were studied: decantation and thickening. The objective is to do an experimental and in a lesser way numerical study to characterize sedimentation the most completly possible with a detailed attention to flow and deposit structure, concentration profiles and determination of sedimentation modes. Used experimental means are the usual techniques of two-dimensional measurement (laser velocimetry and direct visualization) which authorize the data acquisition for configurations where particles evolve in the plan. These laser techniques were improved to simultaneously follow various particles populations and access to various outpouts such as velocities field, local volumic fraction, and velocities of various sedimentation fronts. A simple numerical tool was also built using Stokesian Dynamics and seizing the main part of the physical phenomena driving sedimentation leading to the modeling of the hydrodynamic interactions

APA, Harvard, Vancouver, ISO, and other styles

3

Campos, RogeÌrio. "Three-dimensional reservoir sedimentation model." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421172.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Karl, Joanna Robin. "Gravity Sedimentation: A One-Dimensional Numerical Model." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4594.

Full text

Abstract:

A large fraction of the current cost of wastewater treatment is from the treatment and disposal of wastewater sludge. Improved design, energy efficiency, and performance of dewatering facilities could significantly decrease transport and disposal costs. Dewatering facilities are designed based on field experience, trial and error, pilot plant testing, and/or full scale testing. Design is generally time-consuming and expensive. A full-scale test typically consists_ of side-by-side operation of 4 to 5 full-scale dewatering units for several weeks to more than 6 months. Theoretical modeling of the physics of dewatering units such as the belt filter press, based on laboratory determined sludge properties, would better predict dewatering performance. This research developed a numerical computer model of the physics of gravity sedimentation. The model simulated the gravity sedimentation portion of the belt filter press. The model was developed from a physically-based numerical computer model of cake filtration by Wells (1990). As opposed to the cake filtration model, the inertial and gravity terms were retained in the gravity sedimentation model. Although in the cake filtration model, the inertial terms were shown to be negligible, according to Dixon, Souter, and Buchanan (1985), inertial effects in gravity sedimentation cannot generally be ignored. The region where inertia is important is the narrow interface between suspension and sediment. In the cake filtration model the gravity term was negligible due to the relatively large magnitude of the applied pressure; but in the gravity sedimentation model, since there was no applied pressure, it was necessary to consider the effect of gravity. _ Two final governing equations were developed - solid continuity and total momentum with continuity ("momentum"). ·The finite difference equations used a "space-staggered" mesh. The solid continuity equation was solved using an explicit formulation, with a forward difference in time and central difference in space. The "momentum" equation used a fully implicit formulation with a forward difference in time. The modeler could choose either a central difference or forward difference in space. Non-linear terms were linearized. Boundary Conditions and constitutive relationships were determined. Numerical errors in the numerical model were analyzed. The model was calibrated to known data and verified with additional data. The model was extremely sensitive to the constitutive relationships used, but relatively unaffected by the At or the use of central difference or forward difference for the spatial derivative term in the "momentum" equation. Correlations of the calibrated model to data with a low initial concentration show that the constitutive parameters approximate the data, but not very well. Model runs with low initial concentration required the addition of artificial viscosity to remain stable. The gravity term was always significant, whereas the inertial terms were many orders of magnitude less than gravity. However, the lower the initial concentration, the larger the inertial terms. In addition to the belt filter press, the model can also be applied to cake filtration and design of gravity sedimentation tanks as well.

APA, Harvard, Vancouver, ISO, and other styles

5

Volentik, Alain C. M. "Tephra transport, sedimentation and hazards." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002949.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Carmona, Bardella Ana. "Combining Discrete Element and Process-based sedimentary models: a new tool to model syntectonic sedimentation." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/401652.

Full text

Abstract:

In order to understand the current state of the natural rocky environment and its heterogeneity, we require to study the interaction and time evolution of the numerous geological processes that have contributed to the geological reality we observe today. Given this, the thesis presented here concerns itself with numerical modelling of geological processes. The forward numerical model developed during this thesis is able to simulate deformation and sedimentation in one single setting. To do this, the model uses a novel approach that combines a Discrete Element Model (DEM) and a process- based sedimentary model, Simsafadim (SFM) to link both processes, deformation and sedimentation. The discrete element model (DEM) deals with the simulation of deformation in different materials in 2D and 3D. It is primarily used to investigate the propagation and evolution of deformation in the upper crust caused by tectonic movements. Simsafadim (SFM) is a process-based numerical forward model, which simulates subaqueous clastic transport and sedimentation in three dimensions, including processes of carbonate interaction, production, transport and sedimentation. It can model efficiently the distribution of facies and the depositional architectures in a sedimentary basin and it is a powerful tool for the 3D prediction of stratigraphic structures. Merging both codes provides a new tool for geological modelling in which deformation is influenced by the presence of syntectonic sediment dispersal and deposition. In addition, the tectonic processes change the topographic surface, which influences fluid flow, transport and, consequently, sedimentation in the process-based sedimentary model. The interaction of tectonic and sedimentary processes allows us to study the propagation of deformation in the syntectonic materials as well as how these new sediments influence the propagation of deformation in the pretectonic unit. The model is applied in two different cases studies, in order to test the viability of the new model, as well as to achieve new insight in the respective themes treated: 1) First case study: the effect of normal faulting and a relay ramp on sediment dispersal. The model is used to study the sedimentary infill in an extensional basin, specifically related to a relay ramp system. To perform the test study two configurations are designed: with one normal fault, and with two overlapping normal faults linked by a relay ramp. The different results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin. Nonetheless, when the source area for water and sediment is defined as regional and parallel to the fault, the grain size distribution obtained by the two overlapping faults linked by a relay ramp have clear asymmetries when compared with the ones obtained by one-fault configurations. Therefore, the different extensional experiments allow us to conclude that the configuration with a relay ramp can play an important role in the distribution of the sediments into the basin. 2) Second case study: The effect of syntectonic sedimentation on fold geometry The numerical is used to investigate the effect of syntectonic sedimentation on fold geometry and specifically related to a delta progradation surrounded by two growing anticlines. To the initial tectonic configuration that reproduces the growth of two faults, two different cases of the sedimentary model are considered: without sediments, and considering syntectonic sedimentation. Summing up, the main results obtained for these experiments conclude that the syntectonic sedimentation is controlling the mechanism of fold growth and the final fold geometry: the left-side fold shows a left-vergent asymmetric anticline. Moreover, the strain suggests that this anticline is passing from a detachment fold (without sediments) to a fault propagation fold basinwards (with sediments). As a consequence, the inner syncline and the related sedimentary basin are also changing in transversal and longitudinal direction, being wider with syntectonic sedimentation. El objectiu principal d'aquesta tesi és donar un pas endavant en el coneixement dels processos geològics que intervenen en la formació de les conques sedimentàries mitjançant la creació d'un model numèric per modelitzar la sedimentació sintectònica en un ambient subaquàtic. El model numèric desenvolupat en aquesta tesi és capaç de modelitzar la sedimentació clàstica subaquàtica i la deformació de la unitat pretectònica en una sola configuració. Per fer això, el model combina dos models ja existents: un model d'elements discrets per simular la deformació de la unitat pretectònica (DEM) i un model sedimentari basat en processos, per modelitzar la sedimentació clàstica subaquàtica Simsafadim (SFM). La unió d'aquest dos models, DEM i SFM, proporciona una nova eina per a la modelització geològica. En el nou model, l’evolució de deformació en la unitat pretectònica canviarà la topografia de la conca, que afectarà directament la batimetria, influenciant així els processos de transport i sedimentació que hi tenen lloc. Alhora, aquesta evolució de la deformació de la unitat pretectònica estarà influenciada per la presència dels nous materials sintectònics. Amb aquesta doble interacció tectònica-sedimentària del nou model, també es pot estudiar la deformació en els materials sintectònics. Aquesta nova eina de modelització permet simular i analitzar diferents arquitectures deposicionals sintectòniques i escenaris geològics més complexos. Tant per ampliar el coneixement de com els processos de sedimentació-deformació interactuen en alguns ambients tectònics, com per comprovar l'eficàcia del model, la nova eina s'aplica a dos casos diferents: 1) En primer lloc s'utilitza el model numèric en un ambient extensional per estudiar l'impacte que té la presència de falles normals i les corresponents zones de relleu en la distribució del sediment a la conca. Quan es compara la distribució de sediment obtinguda amb una configuració de dos falles amb una rapa de relleu, amb la distribució de sediment obtinguda amb una configuració d'una sola falla, els resultats mostren asimetries, tant longitudinals com perpendiculars a les estructures. 2) En el segon cas s'estudia l'efecte de la sedimentació sintectònica sobre la geometria final d'un plec. Els resultats, obtinguts a partir de la comparació de l'evolució de les estructures considerant o no considerant sedimentació sintectònica, estableixen que la sedimentació sintectònica pot afectar tant al mecanisme de formació del plec com a la seva geometria final.

APA, Harvard, Vancouver, ISO, and other styles

7

Zhang, Aibin. "CFD Modeling and Optimization of Primary sedimentation tank." Thesis, KTH, Vattendragsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217116.

Full text

Abstract:

In this project, the flow field characteristics of the simplified 2D rectangular primary sedimentation tank in Syvab wastewater treatment plant were achieved by a transient water-air two phases finite-volume method, applying Volume-Of-Fluid (VOF) model. RNG k-ε turbulence model was also employed to calculate the turbulent kinetic energy and its dissipation rate. The undesired hydraulic phenomenon for solid sedimentation was detected in original tank. To reduce the velocity and turbulence intensity of the influent, two categories of optimization methods were proposed, which are installing the baffle and changing the velocity inlet. The modifying effects of different methods were compared by the velocity profiles and the contours of kinetic energy. It turns out that both ways provide a preferred condition for particle settling. In the end, further research was forecasted and the work direction were given. I detta projekt uppnåddes 2D modellering av avloppsflödesfältets karaktär hos en förenklade och rektangulär primära sedimenteringsbassäng, Syvab avloppsreningsverk, genom en transient-tvåfas-finita-volymmetoden med vatten och luft, som tillämpades med Volume-Of-Fluid (VOF) modellen. RNG k-ε turbulensmodellen användes även för att beräkna den kinetiska energin av turbulas och dess dissipationshastighet. Detta för att oönskade hydrauliska fenomen har uppmärksammats hos sedimenteringsbassängen hos avloppsreningsverket. För att minska flödeshastigheten och turbulens föreslås två optimeringsmetoder, vilket är att installera skärm och att ändra inloppets hastighet. Eeffekterna av de olika metoderna jämförs med hjälp av hastighets- och kinetisk energiprofiler. Det visar sig att båda metoderna kan ge gynsammare tillstånd för sedimentering av partikelar. Som avslutning ges prognos för den fortsatta forskningen och arbetsriktningen inom ämnet.

APA, Harvard, Vancouver, ISO, and other styles

8

Sun, Hua. "Digital terrain modelling of catchment erosion and sedimentation /." Title page, contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phs9565.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Zhang, Feng. "Instability in Settling Fibres : A Numerical Study." Doctoral thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141037.

Full text

Abstract:

Sedimenting suspensions exist in a varity of natural phenomena and industrial applications. It is already observed in experiments that the dilute fibre suspensions experience a concentration instability under gravity at low Reynolds numbers. Initially well-mixed suspensions become inhomogeneous and anisotropic due to this instability. This project is focused on the development and validation of numerical models to understand the instability in a dilute fibre suspension by means of the mixture model and the point-particle model. For periodic boundary condition, we use a linear stability analysis to show that inertia and hydro dynamic translational diffusion damp perturbations at long wavelengths and short wavelengths, respectively, leading to a wavenumber selection. However, numerical simulations indicate a weak wavenumber selection even at zero Reynolds number. Numerical simulations also show that the induced flow may either die or saturate on a finite amplitude. The characterof this long time behaviour is dictated by the wavenumber, the presence or absence of the translational diusivity, rotational diffusivity, and the fluid inertia on particle motions. Moreover, the most unstable wavenumber decreases with time and the maximum amplitude increases. The smallest wavenumber obtains the largest amplitude at steady state. For a vessel bounded by sidewalls, the near-wall convection is an upward back flow in the very beginning, due to the combined effects of the steric-depleted layer and a hydrodynamiclly-depleted region near the wall. However, the evolution of the near-wall convection at later times depends on the aspect ratio of the bres, the translational diffusivity and the initial perturbations. The steric-depleted layer in the mixture model can be neglected for large widths. Multiple streamers are obtained due to the sidewalls, implying that the sidewalls can generate a wavelength which is smaller than the channel width. The suspension ends up with a single streamer on one side of the container, consistent with the results of the cases with periodic boundary condition but different from the experimental results. This might be due to the absence of the botton wall in the mixture model. Moreover, the global structure evolution of a suspension is dependent on the width of the vessel and the amplitude ofthe initial perturbations. QC 20140207

APA, Harvard, Vancouver, ISO, and other styles

10

Polorigni, Christian Leprince. "Primary sedimentation tank model with characterized settling velocity groups." Master's thesis, University of Cape Town, 2020. http://hdl.handle.net/11427/32526.

Full text

Abstract:

Primary sedimentation involves the separation of solids and liquid in primary settling tanks (PSTs) of wastewater treatment systems. These physical processes are described by various settling conditions such as discrete and flocculent settling, along with other phenomena such as flocculation, coagulation, ammonification or hydrolysis. The modelling of primary sedimentation has often been overlooked because (i) it involves various intricacies that are difficult to replicate and (ii) primary sedimentation has been assumed to be an input to most of the main unit process models, including the activated sludge (AS) system and the anaerobic digestion (AD) models. Though there has been a wide range of proposed mathematical models to describe how PSTs function, the need to correctly disaggregate the total suspended solids (TSS) into realistic fractions of unbiodegradable particulate organics (UPO), biodegradable particulate organics (BPO) and inorganic settleable solids (ISS), remains. This is because PST models that are unable to correctly split the TSS into its characteristic components make incorrect assumptions. These assumptions lead to inconsistencies in predicting the compositions of the primary sludge (PS) that is fed to the AD unit and the settled wastewater (settled WW) that is treated in the AS system. Hence, it becomes difficult to correctly simulate the entire system (plant-wide) towards a holistic evaluation of system strategies. In this study, a realistic PST model was developed, with characterized settling velocity groups, within a plant-wide setting, for municipal wastewater. This involved the improvement of a current TSS-based model into a more accurate and realistic model that could account for the settling of raw wastewater particles. The model was therefore expected to predict the composition of the PS that is treated in the AD system and the composition of the settled WW that is going to the AS unit processes. This could be achieved by splitting the TSS into UPO, BPO and ISS fractions. In developing preparation of such a realistic PST model, the following objectives were established: 1. Disaggregate the TSS into realistic UPO, BPO and ISS fractions, by means of discrete particle settling modelling (Kowlesser, 2014) and the particle settling velocity distribution (PSVD) approach of Bachis et al. (2015). 2. Verify that the model is internally consistent with wastewater treatment plant (WWTP) data, by means of mathematical material mass balances and other specific scenarios. 3. Demonstrate the application and impact of such a model by performing steady state plant-wide simulations. Using the discrete particle settling approach of Kowlesser (2014), a discrete particle settling model was developed in Microsoft Excel and implemented into a dynamic PST framework in WEST® (Vanhooren et al., 2003). The discrete particle settling model was described using steady state and dynamic calculations and the insights obtained from these calculations were implemented in the current TSS-based PST model of Bachis et al. (2015). This was performed towards developing the University of Cape Town Primary Sedimentation Unit (UCTPSU). The influent raw wastewater TSS was fractionated into UPO, BPO and ISS fractions and settling proportions of these fractions were assigned to five settling velocity groups. In addition, a distinct settling velocity was assigned to each settling velocity group. Previous studies data from WRC (1984) and Ekama (2017), were used in the discrete particle settling model, which was able to reproduce PS and settled WW outputs, through steady state and dynamic calculations and under strict material mass balances. As a result, UPO, BPO and ISS settling proportions as well as settling velocities, were extracted from these calculations and used as input parameters into the UCTPSU model. This dynamic model was rigorously verified to be internally consistent with regards to strict material mass balances. The verification scenarios also included variations of high and low settling velocities as well as a combination of both high and low velocities and checking that the model was behaving as expected. The application and impact of the UCTPSU model were demonstrated using plant-wide scenarios in proposing a preliminary integration, under steady state conditions. It showed how incorrect disaggregation of the TSS into UPO, BPO and ISS fractions can lead to incorrect predictions in terms of the settled WW composition, the AS system capacity, the effluent quality, as well as the energy consumption and generation in the AS system and AD unit respectively. The investigation also revealed the need to measure key wastewater parameters such as particle settling velocities and the unbiodegradable particulate COD fraction, when it comes to realistically modelling of primary sedimentation of municipal wastewater, with the view of optimizing plant operations and tactical decision making. The study thereafter recommended the need to conduct an extensive experimental campaign to measure in-situ diurnal data, mainly in terms of settling velocities and settling proportions of UPO, BPO and ISS. It was also suggested to use the settleometer as a tool to extract these settling velocities and settling proportions, after performing biodegradability tests. As such, the data collected from the experimental campaign and the biodegradability tests could be used in calibrating the UCTPSU model and validation could be undertaken by means of full plant scale data.

APA, Harvard, Vancouver, ISO, and other styles

11

Cooke, Steve Maurice 1959. "A physical model of reservoir sediment bypassing." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277052.

Full text

Abstract:

On average, one percent of reservoir storage capacity is lost annually to sediment deposition in reservoirs. Several methods for sediment removal do exist, but most are inefficient and costly in terms of money or water usage. One method known as siphoning has been shown to adequately remove sediment, but present knowledge is lacking to optimize this method for removal. Three relationships for sediment transport in a pipe were compared against data collected from a physical model resembling a reservoir siphoning system. None of the three accurately predicted the physical model results. However, some trends among the relationships were observed, indicating that with additional modification to the relationships, parameters could possibly be developed to design a prototype system.

APA, Harvard, Vancouver, ISO, and other styles

12

Mitchell, Christabel Anne. "Evaluating the potential for simulating floodplain processes using two-dimensional distributed models." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251185.

Full text

Abstract:

Previous studies of overbank hydraulics and sedimentation have adopted a variety of methods to investigate overbank processes, using either field based, physical or numerical modelling approaches. In this study a two-dimensional depth-averaged model of overbank hydraulics (Hydro2de) is tested and then used to develop a two-dimensional model of suspended sediment transport and deposition. A model grid was used with a higher resolution than those employed in most equivalent model applications in order to represent the topographic complexity of the natural floodplain in detail. The models were calibrated and rigorously tested using a varied and detailed set of spatially and temporally distributed field data. Models were applied to a short reach of the River Culm, Devon, UK. A wide range of field and laboratory data were used to enable model implementation, calibration and validation. Continuous monitoring of stage and sediment concentration were carried out at the site for the period of study and existing data were used from gauging stations located up- and downstream of the site. A large data set of spatially distributed sediment concentration, velocity and flow depth data were collected across the floodplain over a series of flood events. Inundation boundaries were identified using GPS surveys supplemented by field observations and both ground and aerial photography. The amount of overbank deposition was measured for individual floods using astroturf sedimentation traps. Medium-term sedimentation rates were estimated at selected locations using the Caesium-137 whole core technique. Both models were shown to yield good results which, when compared with field measurements were within the limits of uncertainty associated with these data. Simulation results allow a number of conclusions to be drawn about floodplain processes and their representation by numerical models. First, representation of complex, small-scale floodplain topography (features with dimensions <10 m) is of considerable importance when modelling flow and sedimentation on natural floodplains. Second, sediment transfer from the channel to the floodplain is dominated by advection rather than diffusion. Third, low magnitude events are more important than infrequent high magnitude events in terms of total conveyance losses, despite the lower sediment load of the former. Fourth, high resolution distributed models may be used to develop simple conceptual statistical models that capture the complexity of hydraulic conditions on natural floodplains. Finally, further work on floodplain modelling should concentrate on the development of a physically-based understanding of deposition processes in the presence of vegetation.

APA, Harvard, Vancouver, ISO, and other styles

13

Shah, Bashir Hussain. "Land use optimization and sediment yield model for Siran Watershed (Pakistan)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/191104.

Full text

Abstract:

The main objective of this study is an assessment of the potential of applying land use optimization methods for minimizing the sediment yield from catchments. The study area is the Siran watershed, a subwatershed of the Tarbela watershed in Pakistan which drains directly into the Tarbela reservoir. It has an area of 4Ub sq. miles and receives 47.82 inches annual average precipitation. The main land use practices on the Siran Watershed are agriculture, rangeland grazing and forestry. A stochastic model for simulating daily precipitation and another for simulating daily maximum temperatures are developed for the area. The synthetic daily precipitation events are transformed into daily streamflows by the soil moisture counting streamflow model using the synthetic daily maximum temperatures as input. The streamtlow model, called the Generalized Streamflow Simulation System, is modified and used for simulating baseflow recessions. The stochastic precipitation model, the stochastic temperature model and the deterministic streamflow models were combined with the deterministic sediment yield model for simulating sediment yield from the watershed. The modified Universal Soil Loss Equation was used for simulating sediment yield. Parameters at these models were determined from data taken on the Siran Watershed. A linear program was used for land use optimization to minimize sediment yield and maximize watershed production. Both optimization processes ended up with the same land use areas allocating the Maximum area for forests. The expected sediment yield was reduced by 2.5 times and production of watershed was doubled. Optimization of crops was accomplished by maximizing the production of agriculture lands. This resulted in the allocation of major agriculture land areas for apple orchards. By adopting the final optimized land use practices, the sediment yield can be reduced to half and watershed production can be increased six times. The results of the present study are encouraging and indicate that application of land use optimization methods for reducing sediment yields nave great potential on the study area and on other subwatersheds of the Tarbela and Manyla Watersheds. The methodology developed in this study can provide a useful tool for watershed managers to reduce sediment yields and increase the income of the local inhabitants by maximizing the agriculture production in other parts of the country.

APA, Harvard, Vancouver, ISO, and other styles

14

Petticrew, Ellen Lesley. "Sedimentation patterns in nearshore zones of lakes supporting macrophytes." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75898.

Full text

Abstract:

This thesis focuses on three areas of investigation: construction and calibration of gypsum cylinders for the measurement of water flow; quantification of the relationship between flow and macrophyte structure; and the prediction of surficial sediment size structure in the littoral. Near-bottom water flow at 34 littoral sites was quantified using gypsum dissolution. Plant surface area within three weedbeds in Lake Memphremagog (Que. - Vt.) explained 67% of the variance in flow when the effect of water depth was removed. A model relating waterflow within beds to average wind energy and plant surface area was constructed. A multivariate model developed and tested in the littoral of Lake Memphremagog explained 67% of the variance in the proportion of sediment $<$2 um in diameter (clay). The model included the physical variables of fetch, depth, and slope and biological measures of plant presence or absence and sediment organic matter. A second model required plant surface area and sediment organic matter to explain 83% of the variance in the proportion of clay at sites within weedbeds, near the depth of maximum plant biomass.

APA, Harvard, Vancouver, ISO, and other styles

15

Thompson, Mai Phuong. "Statistical modelling of sediment concentration." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26648.

Full text

Abstract:

One technique that is commonly used to replace the costly daily sampling of sedimentconcentration in assessing sediment discharge is the "rating curve" technique. This technique relies on the form of the relationship between sediment concentration and water discharge to estimate long-term sediment loads. In this study, a regression/time-series approach to modelling the relationship between sediment concentration and water discharge is developed. The model comprises of a linear regression of the natural logarithm of sediment concentration on the natural logarithm of water discharge and an autoregressive time-series of order one or two for the errors of the regression equation. The main inferences from the model are the estimation of annual sediment loads and the calculation of their standard errors. Bias correction factors for the bias resulted from the inverse transformation of the natural logarithm of sediment concentration are studied. The accuracy of the load estimates is checked by comparing them to figures published by Water Survey of Canada. Science, Faculty of Statistics, Department of Graduate

APA, Harvard, Vancouver, ISO, and other styles

16

Torrealba, Sebastian Fernando. "A Continuous Mathematical Model of the One-Dimensional Sedimentation Process of Flocculated Sediment Particles." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/755.

Full text

Abstract:

A new continuous one-dimensional sedimentation model incorporating a new continuous flocculation model that considers aggregation and fragmentation processes was derived and tested. Additionally, a new procedure to model sediment particle size distribution (PSD) was derived. Basic to this development were three different parametric models: Jaky, Fredlund and the Gamma probability distribution (GPD) were chosen to fit three different glass micro-spheres PSDs having average particle sizes of 7, 25 and 35 microns. The GPD provided the best fit with the least parameters. The bimodal GPD was used to fit ten sediment samples with excellent results (< 5% average error). A continuous flocculation model was derived using the method of moments for solving the continuous Smoluchowski coagulation equation with fragmentation. The initial sediment PSD was modeled using a bimodal GPD. This new flocculation model resulted in a new general moments’ equation that considers aggregation and fragmentation processes, which is represented by a system of ordinary differential equations. The model was calibrated using a genetic algorithm with initial and flocculated PSDs of four sediment samples and four anionic polyacrylamides flocculants. The results show excellent correlation between predicted and observed values (R2 > 0.9878). A new continuous one-dimensional sedimentation model that resulted in a scalar hyperbolic conservation law was derived from the well-known Kynch kinematic sedimentation model. The model was calibrated using column tests results with glass micro-spheres particles. Two different glass microspheres particle size distributions (PSDs) were used with average diameters of 7 and 37 microns. Excellent values of coefficient of determination (R2 > 0.89, except for one test replicate) were obtained for both the small and large glass micro-spheres PSDs. These results suggest that the proposed sedimentation model can be expanded to model the sedimentation process inside a sediment pond.

APA, Harvard, Vancouver, ISO, and other styles

17

Mallikarachchi, Thanuja D. "Performance Models for Manufactured Stormwater Best Management Practices with Sedimentation and Filtration in Series." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1547131754278262.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Isaksson, Sara. "Simulation of Metal and Metal Oxide Nanoparticle Sedimentation in Solution Using a Computational Model." Thesis, KTH, Skolan för kemivetenskap (CHE), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-206837.

Full text

Abstract:

Nanoparticles are used in many different applications because of their small size and unique properties. The usage is increasing rapidly, which will increase the nanoparticle exposure to the environment. Up till now, environmental behavior and ecotoxicology of nanoparticles have only been studied to a certain extent and because of the increasing usage, research should focus more on nanoparticle behavior and ecotoxicology. An effective way of studying nanoparticles in aqueous environments is to use mathematical models. In this study, the In vitro Sedimentation, Diffusion, and Dosimetry (ISDD) model was investigated and applied to copper, manganese, and zinc oxide nanoparticles to determine their sedimentation velocity in 1 mM NaClO4(aq). The results show that the simulated sedimentation of nanoparticles in solution, i.e. the output from the ISDD model, can vary a lot depending on some of the input parameters in the model. The fact that some of these parameters have to be estimated increases the uncertainty of the ISDD model, although it is possible to yield results in great agreement with experimentally determined sedimentation velocities for the studied systems. The simulation results could always be explained by the theory behind it, which increases the reliability of the ISDD model. The possibility of measuring the effective density of nanoparticle agglomerates using the volumetric centrifugation method was also investigated. This method makes it possible to avoid estimating the fractal dimension, an input parameter with great uncertainty in the ISDD model. The results look promising, although further investigation is needed. The ISDD model seems to be a promising model for future simulation work. The model should be investigated further in order to minimize the uncertainties due to estimations. The possibility to predict nanoparticle sedimentation using a mathematical model will save a lot of time and money, and it can be a helpful tool in the extensive work of identifying the behavior of nanoparticles in aqueous environments.

APA, Harvard, Vancouver, ISO, and other styles

19

Painter, Clayton S. "The Shannon Sandstone new observations and constraints applied to depositional models /." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1799711431&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Payne, Danielle Sarah. "Shelf-to-slope sedimentation on the north Kaipara continental margin, northwestern North Island, New Zealand." The University of Waikato, 2008. http://hdl.handle.net/10289/2413.

Full text

Abstract:

Temperate mixed carbonate-siliciclastic sediments and authigenic minerals are the current surficial deposits at shelf and slope depths (30-1015 m water depth) on the north Kaipara continental margin (NKCM) in northern New Zealand. This is the first detailed study of these NKCM deposits which are described and mapped from the analysis of 54 surficial sediment samples collected along seven shorenormal transects and from three short piston cores. Five surficial sediment facies are defined from the textural and compositional characteristics of this sediment involving relict, modern or mixed relict-modern components. Facies 1 (siliciclastic sand) forms a modern sand prism that extends out to outer shelf depths and contains three subfacies. Subfacies 1a (quartzofeldspathic sand) is an extensive North Island volcanic and basement rock derived sand deposit that occurs at less than 100-200 m water depth across the entire NKCM. Subfacies 1b (heavy mineral sand) occurs at less than 50 m water depth along only two transects and consists of predominantly local basaltic to basaltic andesite derived heavy mineral rich (gt30%) deposits. Subfacies 1c (mica rich sand) occurs at one sample site at 300 m water depth and contains 20-30% mica grains, probably sourced from South Island schists and granites. Facies 2 (glauconitic sand) comprises medium to fine sand with over 30% and up to 95% authigenic glauconite grains occurring in areas of low sedimentation on the outer shelf and upper slope (150-400 m water depth) in central NKCM. Facies 3 (mixed bryozoan-siliciclastic sand) consists of greater than 40% bryozoan skeletal material and occurs only in the northern half of the NKCM. Facies 4 (pelletal mud) occurs on the mid shelf (100-150 m water depth) in northern NKCM and comprises muddy sediment dominated by greater than c. 30% mixed carbonatesiliciclastic pellets. Facies 5 (foraminiferal mud and sand) contains at least 30% foraminifera tests and comprises two subfacies. Subfacies 5a consists of at least 50% mud sized sediment and occurs at gt400 m water depth in southern NKCM while subfacies 5b comprises gt70% sand sized sediment and occurs at mid to outer shelf and slope depths in the northern NKCM. vi A number of environmental controls affect the composition and distribution of NKCM sediments and these include: (1) variable sediment inputs to the NKCM dominated by inshore bedload sources from the south; (2) northerly directed nearshore littoral and combined storm-current sediment transport on the beach and shelf, respectively; (3) offshore suspended sediment bypassing allowing deposition of authigenic minerals and skeletal grains; (4) exchange between the beach and shelf producing similar compositions and grain sizes at less than 150 m water depth; and (5) the episodic rise of sea level since the Last Glaciation maximum approximately 20 000 years ago which has resulted in much sediment being left stranded at greater depths than would otherwise be anticipated. Sedimentation models developed from other wave-dominated shelves generally do not appear to apply to the NKCM sediments due to their overall relative coarseness and their mosaic textural characteristics. In particular, the NKCM sediments do not show the expected fining offshore trends of most wavedominated shelf models. Consequently, sandy sediments (both siliciclastic and authigenic) are most typical with mud becoming a dominant component in southern NKCM sediments only at greater than 400 m water depth, over 350 m deeper than most models suggest, a situation accentuated by the very low mud sediment supply to the NKCM from the bordering Northland landmass.

APA, Harvard, Vancouver, ISO, and other styles

21

Sabetraftar, Karim. "The hydrological flux of organic carbon at the catchment scale : a case study in the Cotter River Catchment, Australia /." View thesis entry in Australian Digital Theses Program, 2005. http://thesis.anu.edu.au/public/adt-ANU20070502.141450/index.html.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Sithebe, Nomcebo Princess. "Flocculation modelling of differential sedimentation based on fundamental physics of settling particles and fractal theory." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/40841.

Full text

Abstract:

Sedimentation is a fundamental operation in wastewater treatment works. A rational design of sedimentation tanks is currently achieved by plotting iso-percentile (iso-percentage) concentration removal profiles from flocculent settling data. A major drawback of the graphical iso-percentage method is that the iso-percentile lines are often manually interpolated and are mere hand drawn estimations. This is because the settling behaviour of sludge particles is highly non-linear. The manual analytical process is therefore very tedious, inaccurate and subjective. Hence, an optimised design of sedimentation tanks is necessary in order to eliminate the errors incurred during data analysis. In this study, a mechanistic iso-percentile flocculent model (referred to as the velocity flocculation model) is developed to simulate the behaviour of flocculating colloidal particles in turbid water. This model is based on the physical meanings of flocculent settling particles and on fractal theory. It is formulated to produce automated iso-percentile curves which are fundamental in the design of sedimentation tanks. The iso-percentile model was vertically integrated into a velocity model to produce a model expressing the velocity of particles as a function of removal rate. The velocity model has an obvious advantage over the iso-percentile model in that it is easy to contextualize. It can be reverted back to the iso-percentile trajectory analysis eliminating the need for extensive data interpolation and may in future eliminate the need for settling column analysis altogether. In the current study, the integrated velocity form is used to predict instantaneous flocculent settling velocity of fine suspended particles under near quiescent conditions. This is vital since it is difficult to obtain velocity values in-situ or directly from sedimentation tanks. Model validity and competency was tested by a direct comparison with existing literature models, such as Ozer’s model and Ramatsoma and Chirwa’s model. Model comparison was based on the goodness of fit, the least sum of square errors and mathematical consistency with known flocculent settling behaviour. The newly developed iso-percentile model achieved a more accurate simulation of physical experimental data, did not violate any of the mathematical constraints and yielded lower sum of square errors than originally achieved by Ozer and Ramatsoma and Chirwa. Notably, the proposed velocity model offers a distinctive advantage over conventional interpolated-iso-percentile based models which are prone to numerical errors during interpolation. Its performance (velocity model) was compared against Je and Chang’s velocity model. Higher velocity values were observed for the new model than for Je and Chang’s model implying that empirically based models would tend to under-predict the velocity values. The model developed in this study brings us one step closer to achieving full automation of the settling tank and clarifier design. Dissertation (MEng)--University of Pretoria, 2013. gm2014 Chemical Engineering unrestricted

APA, Harvard, Vancouver, ISO, and other styles

23

Marrero, Lilian. "Integration of a Sedimentation Module to a Hydrologic Model and its Application to a Mercury TMDL Analysis." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/943.

Full text

Abstract:

This research is part of continued efforts to correlate the hydrology of East Fork Poplar Creek (EFPC) and Bear Creek (BC) with the long term distribution of mercury within the overland, subsurface, and river sub-domains. The main objective of this study was to add a sedimentation module (ECO Lab) capable of simulating the reactive transport mercury exchange mechanisms within sediments and porewater throughout the watershed. The enhanced model was then applied to a Total Maximum Daily Load (TMDL) mercury analysis for EFPC. That application used historical precipitation, groundwater levels, river discharges, and mercury concentrations data that were retrieved from government databases and input to the model. The model was executed to reduce computational time, predict flow discharges, total mercury concentration, flow duration and mercury mass rate curves at key monitoring stations under various hydrological and environmental conditions and scenarios. The computational results provided insight on the relationship between discharges and mercury mass rate curves at various stations throughout EFPC, which is important to best understand and support the management mercury contamination and remediation efforts within EFPC.

APA, Harvard, Vancouver, ISO, and other styles

24

Janes, Victoria Jennifer Julie. "An analysis of channel bank erosion and development of a catchment sediment budget model." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14870.

Full text

Abstract:

Increased sediment loads within river catchments have well-documented detrimental effects on water quality and catchment management plans are required to address reduction and mitigation of these problems. In order to do this it is essential that tools are available that deliver reliable sediment generation data at appropriate temporal and spatial scales. Currently, most sediment generation models do not include bank erosion individually as a sediment source. Therefore, to enable improved accuracy in predictions of future sediment pressures under environmental change, explicit modelling of the rates of sediment production by the bank erosion is required to provide a more complete representation of the catchment sediment budget. In this study, an existing prototype national bank erosion index has been refined. Using Geographical Information Systems (GIS) digitised overlays, channel migration rates were calculated for several UK catchments. Relationships between the rate of channel bank erosion and factors controlling the rates of channel migration were investigated, including channel sinuosity, slope, upstream catchment area, and restriction of migration due to valley width. Significant correlations between bank erosion and sinuosity, upstream area and channel confinement were observed. The non-linear influence of channel planform geometry (curvature and sinuosity) on migration rates was further investigated using an existing meander migration model. A new bank erosion model was developed to incorporate the influence of both channel confinement and sinuosity. As the model incorporates the key physical controls on bank erosion, hence it is expected that it will have wide applicability in catchment- to national-scale bank erosion assessment. A computationally efficient catchment routing model was developed. Data output from a newly developed catchment overland sediment and runoff estimation model (ADAS APT) was used as input to the routing model. The newly developed bank erosion model and an existing floodplain sedimentation model were incorporated within the routing methodology to provide a catchment sediment budget model. The model was applied to the Exe catchment, Devon, UK and validated against observational data. Model estimations of annual sediment generation through bank erosion, sediment deposition on floodplains, and sediment load at the catchment outlet were within the range of observed values. The catchment sediment budget model developed in this thesis provides a more comprehensive representation of catchment sediment processes than existing alternative methodologies.

APA, Harvard, Vancouver, ISO, and other styles

25

Ferbrache, Caleb E. "Finding the Time: Age-Depth Models in Rockshelters and Their Paleoenvironmental Implications." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7698.

Full text

Abstract:

Rockshelters are capable of preserving excellent environmental records within their sediments. But the matter of interpreting an environmental record from rockshelter sediments presents a significant hurdle in the form of dating. An “age-depth model” is typically used to estimate the age of environmental information extending through the deposit. An age-depth model calculates the changes in time between direct ages (like a radiocarbon age) and can provide an estimated age for any depth. While radiocarbon dating can provide an age for organic remains, optically stimulated luminescence (OSL) can provide a direct age on quartz sand deposition and is particularly effective when applied to deposits formed by the wind. This study compares radiocarbon and OSL age-depth models from Last Canyon Cave (LCC) in the Pryor Mountains of south-central Montana. While radiocarbon ages are quite frequently used to construct age-depth models, it is possible they fail to provide accurate ages for the environmental material they aim to date. I re-evaluated the stratigraphy at LCC and then collected OSL samples as well as samples for grain-size analysis from three different sedimentary exposures. Radiocarbon ages had already been produced for one of the exposures (Kornfeld et al. 2012). The OSL samples were most reliable when analyzed on a single-grain level. After creating age-depth models and collecting the grain-size data, I applied ages to all of the grain-size samples according to each of the three age-depth models. Ultimately, the single-grain OSL proved to be fundamentally different than the radiocarbon age-depth model, thereby challenging the current paleoenvironmental reconstruction of the site (Minckley et al. 2015). I conclude that the radiocarbon and single-grain OSL age-depth models were not sufficiently similar, and therefore both dating methods should always be used together when investigating deposits in rockshelters in order to understand how they relate to one another and to the site formation. The use of granulometry also proved to be an important part of reconstruction site formation history. Ultimately, both single-grain OSL and granulometry were determined to be essential parts of studying environmental records in sedimentary deposits in rockshelters.

APA, Harvard, Vancouver, ISO, and other styles

26

Hoe, Tian Hee. "The prediction via a mathematical model of the "primary" self-weight consolidation curve of silt particles during zone settling." Master's thesis, Mississippi State : Mississippi State University, 2001. http://library.msstate.edu/etd/show.asp?etd=etd-11152001-103032.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Bartley, Rebecca. "Quantifying the geomorphic recovery of disturbed streams : using migrating sediment slugs as a model." Monash University, Dept. of Civil Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/8395.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Bryson, Louise Kay. "An erosion and sediment delivery model for semi-arid catchments." Thesis, Rhodes University, 2016. http://hdl.handle.net/10962/2892.

Full text

Abstract:

Sedimentation has become a significant environmental threat in South Africa as it intensifies water management problems in the water-scarce semi-arid regions of the country. As South Africa already allocates 98% of available water, the loss of storage capacity in reservoirs and degraded water quality has meant that a reliable water supply is compromised. The overall aim of this thesis was to develop a catchment scale model that represents the sediment dynamics of semi-arid regions of South Africa as a simple and practically applicable tool for water resource managers. Development of a conceptual framework for the model relied on an understanding of both the sediment dynamics of South African catchments and applicable modelling techniques. Scale was an issue in both cases as most of our understanding of the physical processes of runoff generation and sediment transport has been derived from plot scale studies. By identifying defining properties of semi-arid catchments it was possible to consider how temporal and spatial properties at higher levels emerged from properties at lower levels. These properties were effectively represented by using the Pitman rainfall-runoff model disaggregated to a daily timescale, the Modified Universal Soil Loss Equation (MUSLE) model incorporating probability function theory and through the representation of sediment storages across a semi-distributed catchment. The model was tested on two small and one large study catchment in the Karoo, South Africa, with limited observed data. Limitations to the model were found to be the large parameter data set and the dominance of structural constraints with an increase in catchment size. The next steps in model development will require a reduction of the parameter data set and an inclusion of an in-stream component for sub-catchments at a larger spatial scale. The model is applicable in areas such as South Africa where water resource managers need a simple model at the catchment scale in order to make decisions. This type of model provides a simple representation of the stochastic nature of erosion and sediment delivery over large spatial and temporal scales.

APA, Harvard, Vancouver, ISO, and other styles

29

Hellstedt, Cajsa. "Calibration of a dynamic model for the activated sludge process at Henriksdal wastewater treatment plant." Thesis, Uppsala University, Department of Earth Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-88900.

Full text

Abstract:

För att simulera aktivslamprocessen på ett reningsverk krävs en dynamisk modell som realistiskt beskriver processen. 1987 kom IWA, International Water Association med ASM1, Activated Sludge model no. 1 som fortfarande är den mest använda modellen för att beskriva denna process. I detta examensarbete har ASM1 används för att beskriva aktivslamprocessen på Henriksdals reningsverk i Stockholm. Arbetet har utförts som en del i ett europeiskt projekt, HIPCON (Holistic Integrated Process CONtrol) på IVL, Svenska Miljöinstitutet AB.Arbetet har gått ut på att ta fram en modell som realistiskt beskriver aktivslamprocessen och eftersedimenteringen. För att göra detta har en referensmodell i MATLAB/Simulink använts som grund och byggts om för att likna processen vid Henriksdal. Denna modell i Simulink använder ASM1 för att beskriva aktivslamprocessen. Eftersedimenteringen modelleras med en massbalansmodell där sedimenteringshastigheten beskrivs av en dubbelexponentiell sedimenteringsfunktion. Både ASM1 och sedimenteringsfunktionen använder en mängd olika parametrar för att beskriva processerna och dessa måste kalibreras fram för den process som skall modelleras. Aktivslamprocessen är en biologisk process som beror på en mängd yttre och inre faktorer och är unik för varje reningsverk. Därför finns det inte något enkelt sätt att kalibrera en modell på och information för det enskilda reningsverket i fråga måste tas fram. I detta arbete har två mätkampanjer utförts på Henriksdal för att få mätserier till kalibrering och validering samt information om avloppsvattnets sammansättning. Litteraturstudier har också genomförts för att få information om vilka parametervärden som är av störst intresse för modellen samt i vilket område varje parameter kan förväntas finnas.Arbetet har sedan gått ut på att efter riktlinjer för kalibrering funna i litteraturen ta fram en modell som så realistiskt som möjligt beskriver processen på Henriksdal. Först genomfördes en kalibrering med medelvärden för att hitta jämviktstillstånd och därmed en stabil modell på länge sikt. Utifrån den modellen utfördes sedan en dynamisk kalibrering för att få en modell som beskriver även kortsiktiga och snabba förändringar. Till sist utfördes en validering för att kontrollera om modellen fungerar även för en dataserie som ej använts vid kalibrering. Den framtagna modellen fungerade mycket bra för att modellera medelvärden på lång sikt. För snabba förändringar verkade modellen ligga fel i tiden och troligtvis var den reella uppehållstiden kortare än den teoretiska och bidrar till sämre modellanpassning. To simulate the activated sludge process at a wastewater treatment plant a dynamic model that describes the process is needed. In 1987 IWA, International Water Association presented ASM1, Activated Sludge Model No.1 which still is the most widely used model for this process. In this thesis the ASM1 has been used to describe the activated sludge process. The work is a part of a European project, HIPCON (Holistic Integrated Process CONtrol) at IVL, Swedish Environmental Research Institute.The main objective of the work was to calibrate a model that realistically describes the activated sludge process and secondary sedimentation at Henriksdal wastewater treatment plant in Stockholm. A benchmark model in MATLAB/Simulink was used as a base and rebuilt and extended to fit the process of Henriksdal. In the model ASM1 is used to describe the activated sludge process. The settler is modelled with a mass balance model where the settling velocity is described by a double exponential function. The parameters used in both models have to be calibrated to fit the wastewater treatment plant. To find information about Henriksdal two measuring campaigns were performed to provide data for calibration and validation and to gather information about the composition of the incoming wastewater. From this data a model was developed and calibrated for the process at Henriksdal. After calibration the obtained model worked very well for modelling average values but did not adjust quite as well to fast dynamic changes.

APA, Harvard, Vancouver, ISO, and other styles

30

Ghimire, Ganesh Raj. "Developing Sediment Transport and Deposition Prediction Model of Lower Ohio River near the Olmsted Locks and Dam Area." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1967.

Full text

Abstract:

The present study focuses on the sediment deposition and consequent dredging issues in Lower Ohio River at the Olmsted Locks and Dam area-River mile (RM)-964.4 during the ongoing in-the-wet construction methodology. The study reach is between Locks and Dam 53 (RM 962.6) at upstream, and RM 970 at downstream. One dimensional (1-D) HEC-RAS numerical modeling in conjunction with Arc-GIS was employed. Stream flow measurements, velocity, incoming sediment concentration, bed gradation, and annual hydrographic survey data acquired from public archives of USGS and USACE Louisville District were used as inputs. The model was subjected to the 1-D quasi-unsteady and completely unsteady sediment transport module, available in the latest HEC-RAS 5.0 Beta release. Calibration and validation of the hydrodynamic and sediment models were performed using measured water surface elevation, velocity, and sediment loads at measured sections. Post-model calibration and validation, deposition to excavated cross-sections for future dam shells at Olmsted was predicted, which warrants dredging. The study attempted to analyze the sediment transport trend with the focus on depositionat Olmsted Locks and Dam area using the sensitivity analysis approach of transport capacity functions. Moreover, the capability of 1-D HEC-RAS quasi-unsteady and completely unsteady models were assessed in prediction of sediment deposition in the construction area (dam shells excavation area). A temporal deposition prediction model was developed that can potentially replace the current ad-hoc approach used to determine the dredging schedule. Likewise, a representative environmental risk associated with sedimentation in the study area was examined. The model can potentially be used as a decision support tool to analyze the long term impact of sedimentation in the vicinity of Olmsted Locks and Dam if further updates on the river bathymetry, and specific field data are supplemented to the model.

APA, Harvard, Vancouver, ISO, and other styles

31

Lopes, Vicente Lucio 1952. "A numerical model of watershed erosion and sediment yield." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/191125.

Full text

Abstract:

A physically based, distributed parameter, event oriented, nonlinear, numerical model of watershed response is developed to accommodate the spatial changes in topography, surface roughness, soil properties, concentrated flow patterns and geometry, and land use conditions. The Green and Ampt equation with the ponding time calculation for an unsteady rain is used to compute rainfall excess rates. The kinematic wave equations are used to describe the unsteady one-dimensional overland and channel flow. The unsteady and spatially varying erosion/deposition process on hillslopes and channel systems is described dynamically using simultaneous rates of sediment entrainment and deposition rather than the conventional approach using steady state sediment transport functions. To apply the model the watershed is represented by a simplified geometry consisting of discrete overland flow planes and channel elements. Each plane or channel is characterized by a length, width, and a roughness parameter. For channel elements, a cross-section geometry is also needed. A modular computer program called WESP (Watershed Erosion Simulation Program) is developed to provide the vehicle for performing the computer simulations. Rainfall simulator plots are used to estimate infiltration parameters, hydraulic roughness, and soil erodibility parameters for raindrop impact and overland flow. The ability of the model to simulate watershed response (hydrograph and sedigraph) to a variety of rainfall inputs and antecedent soil moisture conditions is verified using data collected on two small watersheds. The good agreement between the simulated watershed response and the observed watershed response indicates that the governing equations, initial and upper boundary conditions, and structural framework of the model can describe satisfactorily the physical processes controlling watershed response.

APA, Harvard, Vancouver, ISO, and other styles

32

Bussi, Gianbattista. "Implementation of a distributed sediment model in different data availability scenarios." Doctoral thesis, Editorial Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/36534.

Full text

Abstract:

Soil erosion by water can cause agricultural soil losses, desertification, water pollution, reservoir sedimentation, local excess of erosion (such as bridge scour) or deposition, etc. For this reason, the assessment of soil erosion and sediment transport is a key component of integrated catchment management. One of the most useful and up-to-date tools available to catchment managers for soil erosion and sediment transport assessment is distributed modelling. During the last few decades, many sedimentological distributed models were developed and applied for a wide range of climates and basins. Their main advantage is that they allow spatial interpolation or extrapolation of their results. Nevertheless, their use is still limited by some constraints. One of the most relevant limitations to the use of such models is the lack of recorded sediment transport data to be used for model calibration and validation. It is widely recognised that both sediment discharge series and soil erosion measurements are only available in a few and small- to medium-size experimental catchments. The aim of this dissertation is to investigate the possibility of using reservoir sedimentation data as a source of proxy information for sedimentological model calibration and validation. In order to carry out this task, a distributed sedimentological model called TETIS was tested in set of catchments with different sediment data availability. First of all, the TETIS model, developed over the last years by the research group of hydrological and environmental modelling of the Technical University of Valencia, is described, especially focusing on the new features developed within this dissertation (sedimentological sub-model automatic calibration algorithm, small pond sediment retention module, etc.). Then, the model is applied to three catchments with different sediment data availability. The first case-study is the Goodwin Creek catchment (Mississippi, US), an experimental catchment with high sediment transport data availability. The model performance is evaluated, and some considerations are made on the estimation of the sediment volume deposited into the drainage network at the beginning of a rainstorm. The second case-study is the Rambla del Poyo catchment (Valencia, Spain), a medium size semi-arid catchment draining to a coastal lagoon with severe sedimentation problems. The TETIS sedimentological sub-model is calibrated and validated using check-dam sedimentation volumes as an estimator of the total sediment transport. A detailed description of the alluvial stratigraphy infilling a check dam that drains a 12.9 km2 sub-catchment was used as indirect information of sediment yield data. A further application was also developed in this catchment in order to investigate the possibility of calibrating and validating both the hydrological and the sediment sub-models by using reservoir sedimentation volumes and employing neither water nor sediment discharge direct records. The third case-study is the Ésera River catchment (Huesca, Spain), a 1,500 km2 Pyrenean catchment drained by a large reservoir. The depositional history of the reservoir was reconstructed and used for sediment sub-model implementation. The model results were compared with gauged suspended sediment data in order to verify model robustness. The results of this dissertation indicate that TETIS model is a robust tool which provides a reliable reconstruction of the catchment sediment cycle. Its implementation is subject to data availability, both for parameter estimation and for model calibration and validation. Nevertheless, this dissertation proved that sediment records can be replaced by reservoir sedimentation volumes with satisfactory results, taking into account reservoir trap efficiency and sediment dry bulk density. Two modelling approaches were proposed for sediment model implementation, depending on the data availability. These methodologies proved to be consistent and provided a correct estimation of the sediment transport. Nevertheless, further research is needed to address model limitations and to reduce model results uncertainty Bussi, G. (2014). Implementation of a distributed sediment model in different data availability scenarios [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36534 Alfresco

APA, Harvard, Vancouver, ISO, and other styles

33

Hansen, Jacob L. "Utilizing the Public on Public Lands: The Application of Community Science to Monitor and Model Erosion in National Forests." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/etd/3806.

Full text

Abstract:

Unpaved forest roads are adversely affecting coldwater streams through excessive erosion and the subsequent sedimentation of adjacent waterways. To help identify areas of concern, Trout Unlimited (TU) in the Southern Appalachian region developed a Community Science initiative to gather data on sediment sources and stream-road crossings. Volunteers were recruited and trained to monitor road and trail conditions and collect and submit data using a Survey123 application on their cell phones. Analysis of the contributed data reveals statistical connections between drainage type and both erosion level and stream sedimentation. The contributed data were also included as a calibration for the lite version of the Geomorphic Road Analysis and Inventory Package (GRAIP-Lite), a GIS-based road sediment contribution model. The analysis found statistically significant differences between Basic and Calibrated models at one of two sites, and substantial increases in sediment delivery from the Alternate model at both sites.

APA, Harvard, Vancouver, ISO, and other styles

34

Ryherd, Julia Kay. "QUANTIFYING THE RATES AND SPATIAL DISTRIBUTION OF RECENT SEDIMENTATION WITHIN THE HYDROLOGICALLY CONNECTED FLOODPLAINS OF THE MIDDLE MISSISSIPPI RIVER, USA, USING DIGITAL ELEVATION MODELS AND DENDROGEOMORPHOLOGY." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2189.

Full text

Abstract:

The construction of levees along the Mississippi River [MR], beginning in the mid-to-late nineteenth century, have isolated the river along many segments from its floodplain. Sediment from the river is currently deposited in the hydrologically connected floodplain [HCF], the area between the channel margin at low water and the levees. Researchers have studied the amount and rates of sediment deposition along the Upper and Lower Mississippi River segments from the headwaters to Pool 22 and from the Ohio River to the delta; however, no such assessments have been undertaken along the Middle Mississippi River [MMR]. This study attempts to fill the knowledge gap by assessing sedimentation along three islands within the Middle Mississippi River National Wildlife Refuge. On these islands two approaches were undertaken to assess sedimentation along the MMR’s HCF: dendrogeomorphology and the DEM of Difference [DoD] approach. The dendrogeomorphic approach uses tree-ring analyses to document and interpret geomorphic processes and the rates at which they are occurring. The DoD approach subtracts an older DEM from a newer DEM in order to see the change in elevation/depth over time. The geomorphology of the islands and then the entire MMR HCF (from the confluence of the Missouri River to Thebes, IL) were mapped. Using the sedimentation rates for the geomorphic landforms from the three study islands, the sedimentation rates and volumes for the aforementioned portion of the MMR’s HCF were estimated. The estimated volume of sediment was then compared to the MMR’s suspended sediment flux to determine how much of the suspended sediment was going into storage within the MMR’s HCF. The dendrogeomorphic and DoD methods for the study islands yielded average sedimentation rates of 13.3-16.9 mm year-1 and 21.5-80.1 mm year-1, respectively. The rates for the individual landforms on the islands using the dendrogeomorphic results ranged from 5.2 mm year-1 for the splay to 21.8 mm year-1 for the natural levee and splay, with a weighted average of 16.6 mm year-1 for the MMR HCF. Using these rates and the likely range of densities for the floodplain sediments, it is estimated that 4.9-6.6 million metric tons of sediment is accumulating within the MMR annually. This is approximately 5.4-7.4% of the average annual suspended sediment load of the Mississippi River at St. Louis. This means that the MMR is a major sediment sink. If these relatively rapid rates of deposition continue, they have the potential to substantially reduce the HCF’s ability to convey and store flood water which will result in increased flood levels and, consequently, flood risk within the MMR’s levee protected floodplain in the coming decades.

APA, Harvard, Vancouver, ISO, and other styles

35

De, Marchis Hayley. ""The Effects of Ocean Warming and Sedimentation on the Survival and Growth of Acropora cervicornis" and "Differential Prevalence of Chimerism during Embryogenesis in Corals"." NSUWorks, 2017. http://nsuworks.nova.edu/occ_stuetd/463.

Full text

Abstract:

Part I: Coral reefs are essential to coastal economies, protecting coastlines from storms, and harboring high biodiversity. However, reefs are declining due to local anthropogenic stressors and ocean warming. Sedimentation, a local stressor, aggravates the impacts of warming on corals and hinders their survival and growth. Therefore, it is important to investigate whether sedimentation and temperature have a synergistic effect on vulnerable coral species, especially during earlier stages of development. To quantify these effects, survival and growth of newly settled Acropora cervicornis corals were measured at two temperatures (29 and 31°C, representing current and predicted for 2050 Summer temperatures) and three sediment concentrations (30, 60 and 120 mg.cm-2, representing a range from natural sedimentation to dredging conditions). The intent of this study was to mix multiple genotypes to test temperature and sedimentation among genotypic unique individuals. However, only 20% of colonies spawned, and spawning was asynchronous by genotype. Therefore, individuals were produced from self-fertilization. The overall high mortality seen in this study suggests that self-fertilization in A. cervicornis does not produce viable juveniles. Although temperature did not have a significant effect on the survival of self-fertilized juveniles, sediment concentration did. The lowest sediment concentration led to the highest juvenile survival in both ambient and heated conditions. The growth of A. cervicornis selfed individuals was not significantly affected by temperature or sedimentation. These results suggest that reducing sedimentation in dredging and coastal construction areas around coral reefs facilitates the survival of Acropora cervicornis juveniles and may help to ensure their persistence in the future. Because self-fertilized larvae were used, these results need to be interpreted with caution, and this research needs to be repeated with outcrossed A. cervicornis. What is clear is that genotypic diversity is needed for A. cervicornis population growth and resilience. Part II: Chimeras occur when two or more genetically unique individuals of the same species fuse together. The presence of chimerism can aid in the survival and evolution of organisms. This study investigated whether the prevalence of chimerism differs between coral species of different reproduction modes and growth rates. To fulfill this goal, the surface area of egg and/or larvae of three coral species, Montastraea cavernosa, Acropora cervicornis, and Porites astreoides, were measured and compared with the respective surface areas of the newly settled juveniles. This comparison suggested that M. cavernosa displayed a greater tendency to form chimeras than A. cervicornis and P. astreoides. Observations during embryogenesis confirmed this prediction. Montastraea cavernosa is a slow grower and has the smallest eggs of all three study species. Chimerism during embryogenesis may increase this species’ tendency to start the sessile stage at a slightly bigger size and thus increases its competitive abilities for reef space. In contrast, A. cervicornis is a broadcast spawner, fast grower and has a relatively larger egg size, possibly explaining the reduced chimeric tendency during embryogenesis. It is possible that P. astreoides formed chimeras during embryogenesis within the polyp, but they did not form them in the swimming planulae stage. The lack of chimerism during P. astreoides planulae development may be attributed to its brooding reproductive mode, directly releasing large competent larvae that have large initial sizes at settlement. Therefore, the ability to form chimeras in an early developmental stage might provide an ecological advantage to M. cavernosa that contributes to its abundance in Broward County: the greater size at settlement caused by chimerism during embryogenesis may provide this species a competitive advantage for reef space.

APA, Harvard, Vancouver, ISO, and other styles

36

Linde, Tamara Causer. "Relational Database Analysis of Dated Prehistoric Shorelines to Establish Sand Partitioning in Late Holocene Barriers and Beach Plains of the Columbia River Littoral Cell, Washington and Oregon, USA." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1696.

Full text

Abstract:

Studies of episodic shoreline accretion of the Columbia River Littoral Cell (CRLC) have been ongoing since 1964. In this study, the sediment volumes in the late Holocene barriers and beach plains are compiled and formatted in GIS compatible databases for the four sub-cells of the CRLC. Initial evaluation involved the creation of a geodatabase of 160 dated retreat scarp positions, that were identified on across-shore GPR and borehole profiles. Ten primary timelines were identified throughout the CRLC (0-4700 ybp) and those were used to develop polygon cells. Elevation, distance measurements, and position information were all linked to the polygon through a centroid location within the geodatabase. Once the geodatabase was completed, data was imported into MSAccessTM to create a relational database that would allow for examination of the littoral cell in its entirety or of the individual sub-cells. Within the database, sediment volumes, ages, accretion rates, sediment thicknesses, and timeline relationships were calculated and recorded. Using the database, the accretion history of the Columbia River Littoral Cell was evaluated and this examination illustrated the complexity of the system. Northern littoral transport was shown to be an important factor in the development of the littoral cell as a whole. Total sediment volume in the littoral cell was calculated to be 1.74 x 109 m3, with a mean accretion rate of 1.90 x 104 m3/yr, which is significantly less than some previous studies. This is due to a more detailed analysis of the beach and foredune facies themselves. This is likely the result of the higher precision of beach and foredune surface information using LiDAR. The database shows that the developmental history of the CRLC is dependent on temporal and spatial constraints that can be coupled with reverse modeling to predict shoreline erosion trends from impounded river sediments and potential global sea level rise. The North Beaches and Grayland Plains sub-cells have the greatest potential for future erosion; followed by the Clatsop Plains sub-cell.

APA, Harvard, Vancouver, ISO, and other styles

37

Stark, Karolina. "Risk from radionuclides: a frog's perspective : Accumulation of 137Cs in a riparian wetland, radiation doses, and effects on frogs and toads after low-dose rate exposure." Doctoral thesis, Stockholm University, Department of Systems Ecology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-1318.

Full text

Abstract:

Threats from man-made radionuclides include waste issues, increasing number of power plants, underground bomb testing, nuclear weapons, and “dirty bombs”. Until recently the ionizing radiation protection system focused on protecting humans with an implied protection of biota. However, goals of sustainable development and precautionary principles for human activity are leading to an inclusion of plant and animal populations in the protection system.From this perspective, the present thesis examines wetlands that function as sinks for the radionuclide 137Cs, and describes calculated and measured radiation doses to residing biota. Also, multi-level effects from exposure to low-dose rate ionizing radiation were studied. Accumulation of 137Cs after the Chernobyl accident fallout was studied in a riparian wetland with a mean activity concentration of 1 200 kBq m-2 in Sweden (paper I). A mass balance budget of 137Cs showed that the sedimentation of new material was balanced by the decay process of 137Cs in parts of the wetland (paper I).Frogs were identified as organisms of concern in this wetland. Internal radiation doses, based on whole body measurements of frogs, were estimated to be lower than external doses based on soil samples (paper II). Current dose models for biota resulted in a wide range of doses depending on different levels of conservatism in the models. Therefore, in situ measurements with frog-phantoms were found to provide valuable dose information (paper III). Measured doses using frog-phantoms were lower than calculated doses using several dose models. Although a dose conversion factor by FASSET was found to be useful for comparison with measurements in the field. A higher dose was measured to the phantom surface in comparison to inner parts, i.e. the sensitive skin of frogs receives the highest dose. Estimated and measured radiation doses to frogs were below suggested dose rate limits.Low-dose rate 137Cs exposure of eggs and tadpoles from three amphibian species, Scaphiopus holbrookii, Bufo terrestris, and Rana catesbeiana, showed no increased levels of strand breaks in red blood cells, and no effects on development, survival or growth up to metamorphosis (paper IV). The ecological factor larval density had a stronger effect on metamorphic traits than low-dose rate radiation. Higher levels of strand breaks were detected after an acute dose in R. catesbeiana than after a chronic dose supporting a dose rate limit for protection of amphibians rather than a dose limit (paper IV).Based on current knowledge, frogs in the contaminated wetland are probably not exposed to radiation doses from 137Cs that are harmful for the population. However, variations in sensitivity between populations and species, and adaptive responses have been shown for amphibians exposed to other stressors. This supports further research on effects of chronic low-dose rates of ionizing radiation on amphibians.

APA, Harvard, Vancouver, ISO, and other styles

38

Niazi, Erfan. "A Mesoscopic Model for Blood Flow Prediction Based on Experimental Observation of Red Blood Cell Interaction." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38078.

Full text

Abstract:

In some species, including humans, red blood cells (RBCs) under low shear stress tend to clump together and form into regular stacks called rouleaux. These stacks are not static, and constantly move and break apart. This phenomenon is referred to as red blood cell aggregation and disaggregation. When modelled as a single liquid, blood behaves as a non-Newtonian fluid. Its viscosity varies, mainly due to the aggregation of RBCs. The aim of this research is to develop a mesoscale computational model for the simulation of RBCs in plasma. This model considers RBC interaction and aggregation to predict blood-flow characteristics such as viscosity, rouleaux size and velocity distribution. In this work, the population-balance modelling (PBM) approach is utilized to model the RBC aggregation process. The PBM approach is a known method that is used for modelling agglomeration and breakage in two-phase flow fluid mechanics to find aggregate size. The PBM model is coupled to the incompressible Navier-Stokes equations for the plasma. Both models are numerically solved simultaneously. The population-balance equation has been used previously in a more restricted form, the Smoluchowski equation, to model blood viscosity, but it has never been fully coupled with the Navier-Stokes equation directly for the numerical modelling of blood flow. This approach results in a comprehensive model which aims to predict RBC aggregate size and their velocities for different flow configurations, as well as their effects on the apparent macro-scale viscosity. The PBM approach does not treat the microscopic physics of aggregation directly but rather uses experimental correlations for aggregation and disaggregation rates to account for the effects of aggregation on the bulk. To find the aggregation rate, a series of experiments on RBC sedimentation due to gravity is designed. In these tests, aggregated RBCs (rouleaux) tend to settle faster than single RBCs and, due to low shear stresses, disaggregation is very low and can be neglected. A high-speed camera is used to acquire video-microscopic pictures of the process. The size of the aggregates and their velocities are extracted using image processing techniques. For image processing, a general Matlab program is developed which can analyze all the images and report the velocity and size distribution of rouleaux. An experimental correlation for disaggregation rate is found using results from a previous steady-state Couette flow experiment. Aggregation and disaggregation rates from these experiments are used to complete the PBM model. Pressure-driven channel flow experiments are then used for the final validation of the model. Comparisons of the apparent viscosity of whole blood in previous experiments show reasonable agreement with the developed model. This model fills a gap between micro-scale and macro-scale treatments and should be more accurate than traditional macro-scale models while being cheaper than direct treatment of RBCs at the micro-scale.

APA, Harvard, Vancouver, ISO, and other styles

39

BERTHET, CRISTELE. "Ecoulement et transport littoraux tridimensionnel : applications numeriques." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10223.

Full text

Abstract:

L'utilisation d'un modele numerique tridimensionnel a permis d'etudier d'une part un ecoulement caracteristique en zone cotiere a forte bathymetrie, d'autre part, le transport de sediment. L'influence de la bathymetrie et de la stratification sur l'evolution d'un courant et de la surface libre est analysee. Cette etude se concretise par une simulation realiste de la section du courant nord face a la baie de monaco. Le transport du sable et de la vase est considere sous l'action d'un courant et de la houle. Puis, une etude sur le transport des particules organique permet d'evaluer la production primaire dans la colonne d'eau

APA, Harvard, Vancouver, ISO, and other styles

40

Singley, Bradford G. "Computer-Based Instruction for Engineering Education in the Developing World." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2090.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Winkler, Stanislav. "Numerický model proudění vody v horní nádrži Nové Mlýny." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2020. http://www.nusl.cz/ntk/nusl-409740.

Full text

Abstract:

Diploma thesis is focused on understanding problematic of sedimentation in reservoirs with relation on flood episodes. For creating numerical model was necessary to ensure data about morphology of the river, granular composition of the riverbed and hydrology data. In thesis is written how were obtained these documentations, description of creating numerical model in program HEC – RAS 5.0.7. and results of done simulations of real flood episodes, which took place in years 2004, 2005, 2006, 2009, 2013. Output is evaluation each flood episode, description of grain class curves and evaluation of yearly flow before change of riverbed due to transport of sediments and after change of morphology of riverbed.

APA, Harvard, Vancouver, ISO, and other styles

42

Moftakhari, Rostamkhani Hamed. "A Novel Approach to Flow and Sediment Transport Estimation in Estuaries and Bays." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2185.

Full text

Abstract:

Reliable estimates of river discharge and sediment transport to the ocean from large tidal rivers are vital for water resources management, efficient river and harbor management, navigational purposes, and climate analyses. Due to the difficulties inherent in measuring tidal-river discharge, hydrological and sedimentological records are typically too short to adequately characterize long-term (decadal) trends. Also, uncertainties associated with observation and calibration of hydrological models suggest a need for more accurate methods based on longer records of hydrodynamic parameters (e.g. tides). Tidal theory indicates that tides and river discharge interact through quadratic bed friction, which diminishes and distorts the tidal wave as discharge increases. In this study, using tidal constituents, astronomical forcing and a model of the frictional interaction of flow and tides, I propose a novel Tidal Discharge Estimate (TDE) to predict freshwater discharge with an approximate averaging interval of 18 days for time periods with tidal data but no river flow records. Next, using continuous wavelet analysis of tidal properties, I develop a method of estimating river discharge using tides measured on multiple gages along tidal rivers to improve the time-resolution and accuracy of TDE. The applicability of the Multiple-gauge Discharge Estimate (MTDE) is first demonstrated in the two largest tidal-fluvial systems of the Pacific Northwest, the Columbia River Estuary (CRE) and Fraser River Estuary (FRE). A numerical model of an idealized estuary with similar forcing as the FRE and CRE is next run under different hydrologic and morphologic scenarios to evaluate the effect of convergence, friction, and river flow variations on the applicability of MTDE. The TDE method was applied to the San Francisco Bay, using the continuous hourly tide record available since 1858. Results show that TDE reproduces known San Francisco (SF) Bay delta inflows from 1930-present with a Nash-Sutcliffe coefficient of 0.81 and is a useful method for hindcasting historical flows from 1858 - 1929, a period that predates direct measurement of delta discharge. I also recover and digitize ~80 years of Sacramento River daily water level data between 1849 and 1946, from which river discharge to SF Bay is estimated on a daily basis, after adjusting for changes to the river channel. This discharge combined with Net Delta Outflow Index estimates (1930 - 2011) and flow estimates from tidal data (1858 - 2011) provides a more accurate version of SF Bay historic daily inflows from 1849 - 2011. Next, the history of sediment transport and discharge into SF Bay from 1849-present is reevaluated using the daily discharge estimates. A non-stationary rating curve between river flow and sediment transport is developed, with net sedimentation observed during five bathymetric surveys that were used to constrain the total integrated sediment discharge. Results show that ~1600±320 million-tons of sediment have been delivered to SF Bay between 1850 and 2011. There has been an approximately 25 - 30% reduction of annual flow since the 19th century, along with decreased sediment supply. This has resulted in a ~60% reduction in annual sediment delivery to SF Bay. The annual hydrograph of inflow to SF Bay and the seasonality of sediment flux have changed considerably over time, due to both human alteration and climate change. Significant historic spring-melt peak floods have disappeared in the modern system and now peak flows mostly occur in winter. My flow estimation methods also confirm that the flood of January 1862 had the largest daily sediment load and the second largest daily discharge since 1849.

APA, Harvard, Vancouver, ISO, and other styles

43

Malmaeus, Jan Mikael. "Predictive Modeling of Lake Eutrophication." Doctoral thesis, Uppsala University, Department of Earth Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4625.

Full text

Abstract:

This thesis presents predictive models for important variables concerning eutrophication effects in lakes. The keystone is a dynamic phosphorus model based on ordinary differential equations. By calculating mass fluxes of phosphorus into, within and out from a lake, the concentrations of different forms of phosphorus in different compartments of the lake are estimated.The dynamic phosphorus model is critically tested and several improvements are presented, including two new compartments for colloidal phosphorus, a sub-model for suspended particulate matter (SPM) and new algorithms for lake outflow, water mixing, diffusion, water content and organic content of accumulation sediments are implemented. Predictions with the new version show good agreement against empirical data in five tested lakes.The sub-model for SPM uses the same driving variables as the basic phosphorus model, so the inclusion of this model as a sub-model does not require any additional variables. The model for SPM may also be used as a separate model giving monthly predictions of suspended particulate matter in two water compartments and one compartment with SPM available for resuspension in ET-sediments.Empirical data from Lake Erken (Sweden) and Lake Balaton (Hungary) are used to evaluate the variability in settling velocity of SPM. It is found that the variability is substantial and may be accounted for by using a dimensionless moderator for SPM concentration. Empirical data from accumulation area sediments in Lake Erken are used to develop a model for the dynamics of phosphorus sedimentation, burial and diffusion in the sediments. The model is shown to provide reasonable monthly predictions of four functional forms of phosphorus at different sediment depths.Simulations with the lake phosphorus model using two different climate scenarios indicate that lakes may respond very differently to climate change depending on their physical character. Lake Erken, with a water retention time of 7 years, appears to be much more sensitive than two basins of Lake Mälaren (Sweden) with substantially shorter retention times. The implication would be that in eutrophic lakes with long water retention times, eutrophication problems may become serious if the future becomes warmer. This will be important in contexts of lake management when remedial measures against lake eutrophication have to be taken.

APA, Harvard, Vancouver, ISO, and other styles

44

Ipson, Mark K. "Analysis of the Sediment Transport Capabilities of FESWMS FST2DH." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1542.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Hughes, Andrew Owen Physical Environmental &amp Mathematical Sciences Australian Defence Force Academy UNSW. "An assessment of recent changes in catchment sediment sources and sinks, central Queensland, Australia." Awarded by:University of New South Wales - Australian Defence Force Academy. Physical, Environmental & Mathematical Sciences, 2009. http://handle.unsw.edu.au/1959.4/43622.

Full text

Abstract:

Spatial and temporal information on catchment sediment sources and sinks can provide an improved understanding of catchment response to human-induced disturbances. This is essential for the implementation of well-targeted catchment-management decisions. This thesis investigates the nature and timing of catchment response to human activities by examining changes in sediment sources and sinks in a dry-tropical subcatchment of the Great Barrier Reef (GBR) catchment area, in northeastern Australia. Changes in catchment sediment sources, both in terms of spatial provenance and erosion type, are determined using sediment tracing techniques. Results indicate that changes in sediment source contributions over the last 250 years can be linked directly to changes in catchment land use. Sheetwash and rill erosion from cultivated land (40-60%) and channel erosion from grazed areas (30-80%) currently contribute most sediment to the river system. Channel erosion, on a basin-wide scale, appears to be more important than previously considered in this region of Australia. Optically stimulated luminescence and 137Cs dating are used to determine pre-and post- European settlement (ca. 1850) alluvial sedimentation rates. The limitations of using 137Cs as a floodplain sediment dating tool in a low fallout environment, dominated by sediment derived from channel and cultivation sources, are identified. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times) are attributed to the naturally high sediment loads in the dry-tropics. These low increases suggest that previous predictions which reflect order of magnitude increases in post-disturbance sediment yields are likely to be overestimates. In-channel bench deposits, formed since European settlement, are common features that appear to be important stores of recently eroded material. The spatially distributed erosion/sediment yield model SedNet is applied, both with generic input parameters and locally-derived data. Outputs are evaluated against available empirically-derived data. The results suggest that previous model estimates using generic input parameters overestimate post-disturbance and underestimate predisturbance sediment yields, exaggerating the impact of European catchment disturbance. This is likely to have important implications for both local-scale and catchment-wide management scenarios in the GBR region. Suggestions for future study and the collection of important empirical data to enable more accurate model performance are made.

APA, Harvard, Vancouver, ISO, and other styles

46

Moragas, Rodriguez Mar. "Multidisciplinary characterization of diapiric basins integrating field examples, numerical and analogue modelling: Central High Atlas Basin (Morocco)." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/436892.

Full text

Abstract:

The complexity of the interplay between tectonics and sedimentation increases when salt tectonics is involved because of the ductility of salt and its ability to flow. Discrimination between extensional tectonics and salt-related processes is problematic; especially where salt-related rift basins were inverted as occurred in the Central High Atlas in Morocco. The aim of the present work was to analyse and understand the dynamics of the Central High Atlas diapiric basin during the Early Jurassic rift and subsequent post-rift periods using a multidisciplinary workflow integrating fieldwork, analogue models and subsidence and thermal numerical modelling. Two regions were examined to assess the effects of salt tectonics in the evolution of the basin; the Djebel Bou Dahar platform-basin system represented the fault domain of the rift basin where diapiric activity was not described and the Tazoult-Amezraï area and Imilchil diapiric province corresponding to the unstable domain of the basin characterised by the presence of diapiric salt ridges and minibasins. Results from analogue models highlighted the intrinsic interrelation between extension, diapirism and sedimentation that characterised the diapiric domain of the Central High Atlas. Longitudinal and transverse sedimentary progradations and their timing had a strong impact in the migration of ductile layers, in the growth of diapirs and in their lateral structural variations; triggering well-developed passive diapirs in the proximal domains and incipient reactive diapirs or poorly developed roller-like and passive diapirs in the distal domains of the sediment source. Analogue models including post-diapiric compression fairly reproduced the observed structure in the studied areas. Modelling with 6% and 10% of shortening, slightly lower than the Atlas one, produced the progressive close-up of the two flanks of salt walls and their final welding as well as the steepening of their outward flanks, with dips increasing from 8o-17o prior to compression to 30o-50o after compression. Subsidence curves varied depending on the analysed localities of the rift basin. Djebel Bou Dahar showed long-term and low-rate tectonic and total subsidence (0.06 and 0.08 mm yr-1, respectively). The roughly parallel evolution of both total and tectonic subsidence curves indicates the main extensional tectonic influence on subsidence pattern, as corroborated by the syndepositional activity of the outcropping Sinemurian-Pliensbachian normal faults. In the unstable domain, Amezraï minibasin centre showed tectonic and total subsidence rates between 0.06-0.32 and 0.19-0.98 mm yr-1, rates one order of magnitude higher than in the Djebel Bou Dahar. These subsidence rates were up to two-fold their equivalent rates in the Tazoult salt wall (0.01-0.27 and 0.09-0.74 mm yr-1). In the Imilchil diapiric province lateral shifts of the main subsiding depocenters were recorded during Toarcian to Callovian times (tectonic and total subsidence rates up to 0.23 and 0.90 mm yr-1). The subsidence of the unstable domain was caused by the combination of normal fault extension and salt withdrawal from beneath the minibasins during rifting, being the salt-related subsidence predominant during the post-rift and masking the expected subsidence pattern for a rift-post rift transition. For the first time, 27 new vitrinite reflectance data were used to build the thermal evolution and associated geohistory of the Central High Atlas. Thermal models, with heat flows of 105 mW/m2 (from 189 to 140 Ma) followed by 60 mW/m2 and 70 mW/m2 (from 189 to 182.7 Ma) followed by 60 mW/m2, pointed to a post-Middle Jurassic evolution characterised by long-term and low-rate subsidence and an overburden between 1200-2400 m on the Tazoult-Amezraï area. The comparison of subsidence curves from this study with Saharan Atlas and Tunisian Atlas showed that peak of subsidence in these salt-related domains became younger to the east. La discriminació entre processos associats a tectònica extensiva i a tectònica salina es problemàtica; especialment en conques diapíriques extensives invertides com és el cas del Alt Atles Central de Marroc (CHA). L’objectiu d’aquesta tesis és analitzar i entendre els processos que interaccionaren a la conca diapírica del CHA durant el rift Juràssic i el subseqüent període post rift, utilitzant una metodologia multidisciplinària que integra treball de camp, models analògics i models numèrics. S’han estudiat dos dominis de la conca: no diapiric i diapiric (diapirisme durant el Juràssic Inferior i Mitjà). Els models analògics mostren que progradacions longitudinals i transversals i el moment quan s’inicien tenen un gran impacte en la migració dels nivells dúctils, en el mode de creixement diapiric i les seves variacions laterals. Els models amb compressió post-diapírica mostren que dita compressió produeix la reducció progressiva de l’amplada de les estructures diapíriques fins al seu tancament complet, així com a un increment dels cabussaments dels flancs com s’ha observat a les zones d’estudi. Les corbes de subsidència varien segons el domini analitzat. El domini no diapiric es caracteritza per un període llarg de baixes taxes de subsidència tectònica i total (0.06 i 0.08 mma-1). El domini diapiric registra taxes de subsidència tectònica i total fins a un ordre de magnitud majors que en el domini no diapiric (0.23 i 0.90 mma-1) i una migració dels depocentres subsidents. La subsidència del domini diapiric s’interpreta, durant el rift Juràssic Inferior, com una combinació d’activitat de falles normals i migració salina, sent aquesta darrera la predominant durant la fase post-extensiva i emmascarant el patró de subsidència esperat en un estadi de transició rift-post rift. Per primera vegada, es presenta la geohistòria de la part central del CHA. Els models tèrmics emprats per a la seva construcció, avaluats amb 27 noves dades de reflectància de vitrinites de la zona d’estudi, suggereixen una evolució post-Juràssic Mitjà caracteritzada per un període llarg de baixa subsidència que hauria enterrat la regió entre 1200-2400 m, en comptes de una complexa historia que inclouria diversos esdeveniments d’exhumació com s’ha enregistrat en altres zones del Alt Atles Marroquí.

APA, Harvard, Vancouver, ISO, and other styles

47

Rodrigues, Miriam Fernanda. "Dinâmica hidrossedimentológica de pequenas bacias hidrográficas florestais." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/3796.

Full text

Abstract:

Areas cultivated with eucalyptus forests have increased in Southern Brazil, and the effects on hydrosedimentological processes are not well known particularly at the watershed scale and in watersheds where land use has been changing. The Soil and Water Assessment Tool (SWAT) model has been applied in a few forested watersheds to evaluate and predict effects of commercial forest cultivation or land use change in hydrological processes, whilst erosion processes has not been the main goal. The present study aimed (i) to evaluate the effects of eucalyptus plantation on hydrosedimentological processes, and to evaluate the efficiency and limitations of the Soil and Water Assessment Tool (SWAT) model to simulate streamflow and sediment yield (daily and monthly) in nested eucalyptus watersheds and in two paired watersheds with eucalyptus and grassland, and (ii) to identify the contribution of the bank channel, unpaved roads and eucalyptus stands sediment-sources for two different size fractions of sediment (< 0.063 mm and 0.063-2 mm) deposited along the drainage network, and suspended sediment collected in the outlet of small watersheds. SWAT was used to evaluate hydrological and erosion processes for two nested forest watersheds (watershed-0.98 km2 and sub-watershed-0.39 km2) and two paired watersheds in Pampa Biome, one with grassland (1.10 km2) and other with eucalyptus (0.83 km2). Measured streamflow and sediment yield at the watersheds outlets was used to evaluate model sensitivity to selected model parameters, and for calibration from 2009 to 2013 for nested watersheds, and from 2009 to 2013 for paired watersheds. Time series plots and standard statistical measures were used to verify model predictions. For nested watersheds, predicted monthly streamflow was very good during calibration for the watershed and for the sub-watershed, respectively. Predicted monthly sediment yield was very good and satisfactory for the watershed, and unsatisfactory for the sub-watershed. Simulations for daily time-scale were satisfactory to predict streamflow and sediment yield for the watershed. For the sub-watershed, predicted streamflow was satisfactory , but sediment yield was unsatisfactory . For paired watersheds, predicted monthly streamflow was good during calibration for the grassland watershed and for the eucalyptus watershed. Predicted monthly sediment yield was satisfactory for the grassland watershed, and very good and satisfactory for eucalyptus watershed. Daily simulations were satisfactory to predict streamflow in both grassland and eucalyptus watersheds. The results suggest that the SWAT model is a promising tool to evaluate hydrological processes in Brazilian watersheds. However, more field work with continuous monitoring is required and empirical equations of SWAT must change to better represent the processes that predominate in each watershed and to represent the hydrological and erosion processes in sub-daily time-scale and, especially, for small watersheds where the time of concentration is less than one day. Sediment-sources was evaluated using geochemical properties, determined by inductively coupled plasma mass spectrometry and X-ray fluorescence analyses, and the data used to calculate proportional contributions of sediment. Source contributions were determined at points spatially-distributed along the main channel of the watershed. Source determination for in-stream sites was done using samples collected in one spot to evaluate source-contribution of area upstream of this site of interest to indicate how different sources dominate at different downstream locations. To examine whether different size-fractions shared similar origins, two size fractions of both source and suspended samples including fine (<0.063 mm) and coarse (0.063 2 mm) particles were analyzed. Fingerprinting approach indicated particle-size and location of sources within a watershed are major factors affecting the measured contribution of sources for coarse and fine sediments. The closer a sediment sampling site is to a potential source, the more likely this sediment-source will dominate the sampled material, especially for coarse particles. Based on the classification analysis, the relative contribution of each source to eroded sediments was bank channel, i.e. from the stream network. Modeling results and sediment-source identification can provide an improved understanding effect of land use or change in land use on sediment yield in watershed scale, which are useful and may be used as a management tool of natural resources. Áreas cultivadas com florestas de eucalipto têm aumentado no Sul do Brasil e os efeitos sobre os processos hidrossedimentológicos são pouco conhecidos, especialmente em escala de bacia hidrográfica e para áreas em que ocorreu mudança no uso do solo. O modelo Soil and Water Assesment Tool (SWAT) tem sido utilizado em bacias hidrográficas florestais para avaliar e simular o efeito do cultivo de florestas comerciais ou mudança de uso do solo sobre os processos hidrológicos, mas os processos erosivos não têm sido avaliados. O presente estudo objetivou (i) avaliar os efeitos do plantio de eucalipto sobre os processos hidrossedimentológicos e a eficiência e as limitações do SWAT em simular o escoamento superficial e produção de sedimentos (diários e mensais) em bacias hidrográficas embutidas, ocupadas com eucalipto, e em duas bacias hidrográficas pareadas ocupadas principalmente com eucalipto e com campo natural, e (ii) identificar a contribuição das fontes margem da rede de drenagem, as estradas e os povoamentos de eucalipto na geração de duas diferentes frações de sedimentos (< 0,063 mm e 0,063-2 mm) depositados ao longo da rede de drenagem, e de sedimentos em suspensão coletados no exutório de bacias embutidas. O SWAT foi utilizado para avaliar os processos hidrológicos e de erosão em duas bacias florestais embutidas (bacia-0,94 km2 e sub-bacia-0,39 km2) e em duas bacias hidrográficas pareadas no Bioma Pampa, uma com campo natural (1,10 km2) e outra com eucalipto (0,83 km2). A vazão e a produção de sedimentos medidas nas seções de monitoramento das bacias hidrográficas foram utilizadas para avaliar a sensibilidade dos parâmetros selecionados do modelo e para calibração para as bacias embutidas (2009-2013), e para as bacias pareadas (2009-2013). As séries temporais e os parâmetros estatísticos foram utilizados para avaliar o potencial preditivo do modelo. Para as bacias embutidas, a representação da vazão mensal foi muito boa durante a calibração para a bacia e para a sub-bacia, respectivamente. A representação da produção de sedimentos mensal foi muito boa e satisfatória para a bacia, e insatisfatória para a sub-bacia. As simulações na escala diária foram satisfatórias para a representação da vazão e da produção de sedimentos para a bacia. Para a sub-bacia, a representação da vazão foi satisfatória, mas da produção de sedimentos foi insatisfatória. Para as bacias hidrográficas pareadas, a representação da vazão mensal foi boa durante a calibração para a bacia com pastagem e para a bacia com eucalipto. A representação da produção de sedimentos mensal foi satisfatória para a bacia com pastagem, e muito boa e satisfatória para a bacia com eucalipto. As simulações diárias foram satisfatórias para a vazão em ambas as bacias pareadas. Os resultados sugerem que o modelo SWAT é uma ferramenta promissora para avaliar processos hidrológicos em bacias hidrográficas brasileiras. No entanto, fazem-se necessários mais tempo de monitoramento contínuo das variáveis hidrossedimentológicas e alteração de equações empíricas do SWAT para melhor representar processos erosivos que predominam em cada bacia e para representar os processos hidrológicos e erosivos em escala sub-diária, especialmente para pequenas bacias em que o tempo de concentração é menor do que um dia. As fontes de sedimentos foram avaliadas por meio do uso de propriedades geoquímicas, determinadas por análises de espectrometria de massas com plasma e de fluorescência de raios-X. A contribuição das fontes de sedimentos foi determinada em pontos espacialmente distribuídos ao longo do canal principal da bacia. Amostras de sedimento de um ponto de coleta foram utilizadas para avaliar a contribuição das fontes da área de contribuição à montante desse local de interesse e para indicar o a diferença da contribuição dessas fontes em diferentes localizações à jusante. Para avaliar se as diferentes frações de sedimentos tem origem semelhante, duas frações de tamanho de partículas das fontes e amostras de sedimento fino (< 0,063 mm) e grosso (0,063-2 mm) foram analisadas. A técnica fingerprinting indicou que o tamanho das partículas e localização das fontes dentro da bacia hidrográfica são os principais fatores que afetam a contribuição das fontes para a produção de sedimentos finos e grossos. As fontes mais próximas do local de amostragem são as potenciais fontes de sedimentos, sendo provável que essa fonte de sedimentos será dominante na amostra de sedimentos, principalmente para as frações grossas. Com base na análise de classificação, a contribuição relativa de cada fonte indicou que a principal fonte de sedimentos foi a margem do canal da rede de drenagem. Os resultados da modelagem e identificação das fontes de sedimentos contribuem para uma melhor compreensão do efeito do uso do solo ou da alteração no uso sobre a produção de sedimentos na escala de bacia hidrográfica, que são úteis e podem ser utilizados como ferramenta de gestão dos recursos naturais.

APA, Harvard, Vancouver, ISO, and other styles

48

Pattison, Zarah. "Effects of invasive alien plants on riparian vegetation and their response to environmental factors." Thesis, University of Stirling, 2016. http://hdl.handle.net/1893/25404.

Full text

Abstract:

Biological invasions are reportedly one of the major contributory factors to biodiversity loss worldwide. The impacts of invasive alien plant (IAP) species on native communities are widely documented in the scientific literature, however, there is still a lack of detailed information on their impacts within the most vulnerable habitats. Riparian habitats are highly dynamic systems and naturally disturbed, making them particularly vulnerable to invasion. Climate change, directly or indirectly, is also predicted to adversely impact river systems, which may subsequently alter invasion rates and the impacts of IAPs. However, the interactions between climate and IAPs and their combined effects on vegetation have rarely been examined. To address these knowledge gaps, this thesis investigates: (1) the role of environmental variables, such as sediment loading or climate-related changes to river flow regime, on the abundance of IAPs within riparian zones; (2) how variation in IAP abundance impacts native vegetation, relative to the effects of native dominant plant species and (3) some of the mechanisms underlying the effects of IAPs in riparian habitats. Historic and recent field survey data were used to investigate changes in riparian vegetation on British rivers during the last 20 years. Analyses indicate that IAPs had a negative but small effect on native plant diversity. Overall, changes in land use and differences in flow regime between recording periods were the most important predictors of plant community change. Specifically, IAPs had a greater probability of being present along lowland rivers that experienced increased frequency of high flow events. On a local scale across rivers in Scotland, the abundance of IAPs was constrained by greater soil moisture in summer, whilst greater abundance was associated with tree-lined banks. Both native dominant species and IAPs negatively affected subordinate species abundance to a greater extent than species richness, although this effect varied spatially with bank elevation. Artificial turf mats were used to quantify viable propagules within riverine sediment deposited over-winter along invaded riverbanks. The data indicate that there is a legacy effect of IAP abundance, with the most invaded sites being associated with higher sediment loading the following year, though, contrary to the general pattern, 12 sediment associated propagules were scarcer at invaded sites. Moreover, lower above-ground native diversity was associated with sites which had been previously invaded. Plant species composition in the propagule bank and above-ground vegetation were highly dissimilar, particularly closest to the water’s edge at highly invaded sites. This suggests that mono-specific stands of IAPs proliferate best under less disturbed environmental conditions, although fluvial disturbance events may be required to create opportunities for initial establishment. The propagule bank contributed very little to the above-ground vegetation, nor did it limit invasion, suggesting that above-ground plant composition is largely dictated by competitive interactions. The findings presented in this thesis suggest that invasion by IAPs is an additional stressor for native vegetation within riparian habitats, modifying above-ground plant communities via competition and suppressing recruitment from the propagule bank. However, native dominant species common in riparian habitats also negatively impact, subordinate species via competition, in some cases equalling the effect of IAPs. Native dominant and IAP species are differently affected by environmental factors operating in the riparian zone, which may provide future opportunities for reducing and managing invasions.

APA, Harvard, Vancouver, ISO, and other styles

49

Bongono, Juilien. "Caracterisation des suspensions par des methodes optiques. modelisation par reseaux de neurones." Thesis, Saint-Etienne, EMSE, 2010. http://www.theses.fr/2010EMSE0577/document.

Full text

Abstract:

La sédimentation des suspensions aqueuses de particules minérales microniques, polydisperses et concentrées a été analysée à l’aide du Turbiscan MA 2000 fondé sur la diffusion multiple de la lumière, en vue d’établir la procédure qui permet de déceler la présence d’une morphologie fractale, puis de déduire les règles de comportements des suspensions fractales par la modélisation avec les réseaux de neurones. Le domaine des interactions interparticulaires physicochimiques (0 à 10% volumique en solide) a été privilégié.La méthodologie de détermination de la structure multifractale des agglomérats et de la suspension a été proposée. La modification structurale des agglomérats qui est à l’origine de comportements non linéaires des suspensions et qui dépend des propriétés cohésives des particules primaires, est interprétée par la variation de la mobilité électrophorétique des particules en suspension. Une approche d’estimation de ces modifications structurales par les réseaux de neurones, à travers la dimension fractale, a été présentée. Les limites du modèle à assimiler ces comportements particuliers ont été expliquées comme résultant du faible nombre d’exemples et de la grande variabilité des mesures aux faibles fractions volumiques en solide The sedimentation of aqueous suspensions of micron-sized mineral particles, polydisperses and concentrated, was analyzed using the Turbiscan MA 2000 based on the multiple light scattering in order to establish the procedure to detect the presence of a fractal morphology, and then to deduce the set of laws of fractal behavior of suspensions by modeling with neural networks. The methodology for determining the multifractal structure of agglomerates and the suspension was proposed. The structural modifications of the agglomerates at the origin of the nonlinear behavior of suspensions and which depends on cohesive properties of primary particles, is interpreted by the change of the electrophoretic mobility of suspended particles. The estimation by neural networks of these structural changes, through the fractal dimension has been presented. The limits of the model to learn these specific behaviors have been explained as resulting from the low number of examples and the great variability in the measurements at low volume fractions of solid

APA, Harvard, Vancouver, ISO, and other styles

50

Yang, Junqing. "Assimilation de données variationnelles pour les problèmes de transport des sédiments en rivière." Université Joseph Fourier (Grenoble), 1999. http://tel.archives-ouvertes.fr/tel-00004863.

Full text

Abstract:

La prévision de la sédimentation d'une rivière requiert l'utilisation d'un modèle mathématique régissant l'écoulement et de données d'observation. Le but de ce travail est de proposer une méthode d'assimilation de données qui permet de reconstituer les champs en tenant en compte du modèle et des données d'observation. La méthode qui est proposée est fondée sur les techniques de contrôle optimal. On présente les problèmes de sédimentation et leurs approximations numériques, un algorithme de décomposition est introduit et sa convergence est étudiée. En préalable à l'exploitation à des problèmes réels, on a vérifié la faisabilité de la méthode variationnelle d'assimilation de données pour trois types de problèmes de transport des sédiments : 1) la détermination de la condition initiale, 2) l'identification des paramètres, 3) l'estimation de l'erreur de la modélisation. Les études de sédimentation sur le terrain conduisent à des problèmes numériques de très grande dimension, dans une dernière partie on s'est intéressé à des techniques permettant la réduction de l'espace de contrôle pour obtenir des problèmes d'une taille raisonnable

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Sedimentation modes'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles